Kinetic and isotopic studies on the reaction of nitrous acid with cis-chlorobis(ethylenediamine)(hydroxylamine)cobalt(III)

Abstract

Nitrous acid reacts with the title complex giving N₂O and N₂, the former gas being the major product. At [H⁺] > 0.1 mol dm^–3 the rate law is Rate α[H⁺][HNO₂][complex], while at lower acidities the reaction is retarded by H⁺ with a rate law: Rate ∝[H⁺]^–1[HNO₂][complex]. At [H⁺]ca. 0.1 mol dm^–3 there are deviations from these rate laws. The corresponding complex with O-methylhydroxylamine does not react with HNO₂. The reaction at higher acidities is assumed to involve rate-determining formation of an O-nitroso-species, NH₂ONO, which undergoes re-arrangement to give a co-ordinated hyponitrite species which either decomposes to N₂O or reacts via a nitrous acid-catalysed reaction to give N₂. The rate law containing the [H⁺]^–1 term is less easy to interpret, and may involve attack of the nitrosating agent on a doubly deprotonated complex.